Breath sound generator

ABSTRACT

Apparatus is described for generating electrical signals having the same general waveform as the waveform of the sound produced by human breathing. The apparatus comprises a sinusoidal generator, means for adding a DC bias to said sinusoidal wave, means for accepting the two polarities of the sinusoidal wave, means for operating on the two halves separately, and means for combining the two halves into a single waveform and using that waveform to modulate a white noise source.

United States Patent Inventor Robert M. Eisenberg References Cited WWW",UNITED STATES PATENTS gm gtz'a i 3,384,981 5/1968 Baessler et al. 35 17Patemed Sept. 14, 1971 3,508,347 4/1970 Keefer 35/17 AssigneeSinger-General Precision Inc. Primary Examiner-Harland S. SkogquistBinghamton, N.Y. AttorneysFrancis L. Masselle and William Grobman i A vt ABSTRACT: Apparatus is described for generating electrical signalsSawing the same genera! waveform as the waveform of BREATH SOUNDGENERATOR the sound produced by human breathing. The apparatuscomlocla'ms Drawmg prises a sinusoidal generator, means for adding a DCbias to US. Cl 35/17, said sinusoidal wave, means for accepting the twopolarities of 332/31 R the sinusoidal wave, means for operating on thetwo halves Int. Cl G091) 23/28 separately, and means for combining thetwo halves into a sin- Field of Search 35/17, 19 gle waveform and usingthat waveform to modulate a white W R, 31 T, 37 R noise source.

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I 2? I l NOISE T IN 2s PATENTEDSEPMISYI $604,129

SHEET 1 OF 2 INVENTQR.

ROBERT M. E/SE/VBERG BREATH SOUND GENERATOR This invention relates to asystem for generating electrical signals which can be used to duplicatesounds produced in the human body.

As the population of the world increases, the need for additionalmedical help also increases. Partially because of the long time requiredfor the training of such individuals, there has been a substantialshortage of trained medical personnel throughout the would for a numberof years. In order to increase the number of individuals trained eachyear, research has been conducted to change and improve the methods ofeducating such personnel. As with many other complex fields, thetraining of medical students is leaning more and more upon mechanicaltraining aids, such as simulators.

In the past it has been difficult to simulate the operation of the humanbody in a manner suitable for training medical personnel. One of thereasons for this difficulty is the problems encountered in designingapparatus which functions as a normal body would but which also permitsthe insertion of malfunctions. The malfunctions must, of course, becontrolled and must duplicate those which are ordinarily found in bodilymalfunctions.

It is an object of this invention to provide a new and improved systemfor duplicating human body sounds.

It is another object of this invention to provide a new and improvedapparatus for duplicating the sound of breathing.

It is a further objectof this invention to provide a new and improvedapparatus for duplicating the sound of human breathing, both normal andabnormal.

It is still another object of this invention to provide a new andimproved electrical device for generating electrical signals having anenvelope similar to the envelope of the sounds produced by breathing.

Other objects and advantages of this invention will become more apparentas the following description proceeds, which description should beconsidered together with the accompanying drawings in which:

FIG. 1 is a curve which illustrates the waveform to be duplicated;

FIG. 2, 3, 5, 6, and 7 are waveforms for explaining the operation of theapparatus of this invention;

FIG. 4 is a schematic circuit diagram of apparatus according to thisinvention;

FIG. 8 is a schematic circuit diagram of apparatus for generatingabnormal breath sounds; and

FIGS. 9 and 10 are additional waveforms generated by the apparatus ofthis invention.

Referring now to the drawings in detail and more particularly to FIG. I,a curve is shown which generally duplicates the waveform of the sound ofnormal breathing. The curve of FIG. 1 is symmetrical about a zero line.The abscissa of this chart represents time, and ordinate representsamplitude. Several complete cycles are shown each comprising two parts,a first part 11 and a second part 12. The curve is actually themodulation envelope of noise 13 which is amplitude modulated. A completecycle of the breathing sound comprises the two parts 11 and 12, where 11represents the sound generated in inhaling and the portion 12 representsthe sound generated while exhaling. Neither of the portions 11 or 12comprises a half cycle, and the portion 12 is substantially longer thanthe portion 11.

In generating a signalwhich approximates that shown in FIG. I, one ofthe first steps performed in this invention is to provide a sine wavehaving the same wavelength L as a complete cycle such as shown inFIG. 1. In FIG. 2, the envelope of the curve of FIG. 1 is shown after ishas been rectified, and only the upper half is shown. The two parts aredesignated 11 and 12 as they also are designated in'FIG. 1. Shownsuperimposed upon the two portions 1 l and 12 in FIG. 2 is a sine wave14 to illustrate that a complete cycle of the sine wave 14 is equivalentto a complete cycle of the breathing sound. As shown in FIG. 2 bothwaves are symmetrical about the zero axis 15, but even though the sinewave 14 is a good start toward developing the desired waveform, itsshape does not begin to approximate even half of the envelope as shownin FIG. 2.

However, displacing the zero axis 15, as shown at 14 in FIG. 3, the sinewave 14 can be given the same crossover points as the breathingwaveform. In FIG. 3 the upper portion of the breathing envelope,designated 11 and 12, is shown and the sine wave 14 is shown in anupwardly displaced zero axis 16. By moving the axis 15 to the newposition shown at 16, the points at which the sine wave 14 intersect theaxis 16 can be made to coincide with the points at which the breathsound envelope also cross the axis 16. This means that a complete cycleof the sine wave I4 is now broken into two parts which are unequal insize but which coincide in length with the two parts 11 and 12 with thebreath sound envelope. It is now necessary to modify the shapes of thesetwo portions so that they are similar in shape to the two portions lland 12.

To accomplish this entire process the circuit shown in FIG. 4 has beendevised. An oscillator 21 feeds its output through a resistor 22 to thejunction of a pair of diodes 26 and 27. This junction is connectedthrough a resistor 23 to the slide contact 25 of a potentiometer 24. Oneend of the potentiometer 24 is connected to ground and the other end isconnected to a source of positive potential. The anode of the diode 27is connected to the cathode of the diode 26, and the cathode of thediode 27 is connected through a capacitor 28 to ground and through apotentiometer 29 to the base electrode of transistor 36. The anode ofthe diode 26 is connected through a resistor 31, an amplifier 32, and aresistor 34 to the base electrode of the transistor 36. The baseelectrode of the transistor 36 is also connected through a resistor 38to a potentiometer 39, one end of the potentiometer 39 being groundedand the other end being connected to a source of negative potential. Thetransistor 36 has its collector electrode directly to the source ofpositive potential and also to the collector electrode of a transistor37. The emitter electrode of the transistor 36 is directly connected tothe base electrode of the transistor 37. The emitter electrode of thetransistor 37 is connected through a resistor 41 to a source of negativepotential and to one input of an amplitude modulator 44. The modulator44 has an input terminal 45 adapted to be connected to a source of whitenoise, and the output from the modulator 44 is taken from a terminal 46across an output resistor 43.

In operations, the output from oscillator 21 is applied to the junctionof the pair of diodes 26 and 27. At the same time, the junction betweenthe two diodes 26 and 27 is also connected through the potentiometer 24to the source of positive potential so that an adjustable potential canbe applied to the two diodes 26 and 27 to bias them. Actually, thejunction formed by the resistors 22 and 23 serves to add the potentialfrom the source of positive potential and the output of the oscillator21 so that the zero line of the oscillatory output from the oscillator21 is moved out of the line of symmetry of that wave. Thisnonsymmetrical sine wave is rectified by two diodes 27 and 26 and theresultant waveforms are shown in FIGS. 5 and 6. The rectified positiveportion 17 of the sine wave shown in FIG. 5 is that which passes throughthe diode 26 and is applied to the amplifier 32. The negative portion 18of the sine wave shown in FIG. 6 is the portion rectified by the diode27 and is applied to the potentiometer 29. The resistor 34 and thepotentiometer 29 provide a summing network with the potentials in thetwo paths being added together at the junction point 35. The amplifier32 inverts the positive portion 17 which passes through the diode 26 sothat the potentials applied to the junction between 35 are of the samepolarity. These potentials are also applied to the base electrode of thetransistor 36 which is connected together with transistor 37 in aDarlington circuit. FIG. 7 shows the combined waveform but does not showthe effect of the capacitor 28 which is used to lengthen the curve 18and to decrease its amplitude. The capacitor 28, operating with thepotentiometer 29, serves to integrate the negative portion of thewaveform 18. The output from the Darlington amplifier is taken acrossthe resistor 41 and is applied to the modulator 44. The other input,which is the carrier and may be supplied from any source of noise suchas a white noise generator, is applied to the input terminal 45 of themodulator 44. The signal applied to the modulator 44 from the transistor37 modulates the amplitude of the noise potentials applied to inputterminal 45. At the same time, the modulator 44 converts the half-wavesignals shown in FIG. 7 into full-wave signals which are symmetricalabout a central axis and which are similar to those shown in FIG. 1. Inaddition to its use as a summing resistor and its operation with itscapacitor 28 as an integrator, the potentiometer 29 may also be used toadjust the relative amplitude between the two portions 17 and 18 of thecomplete cycle. The modulator 44 may be any suitable amplitude modulatorwhich will amplitude modulate the noise input with the waveform fromtransistor 37.

As indicated above, the addition of pathological sounds sounds whichduplicate the abnormal activities of bodily organsis important to thetraining objectives of the apparatus of this invention. A circuit forproducing and adding one type of such sounds, by way of example, isshown in FIG. 8. The malady whose sound is duplicated by the circuit ofFIG. 8 is called rales, a main identifying feature of which is arasping, varying low frequency sound generated principally uponexhalation. In FIG. 8 an input terminal 51 is adapted to be connected tothe output of the amplifier 32 in FIG. 4. The terminal 51 is connectedthrough a switch 52, a resistor 53, and a capacitor 54 to ground. Thejunction of the resistor 53 and the capacitor 54 is connected to theemitter electrode of a unijunction transistor 55 whose base 2 electrodeis connected through a resistor 56 to a terminal 57 which is connectedto a source of positive potential. The base 1 electrode of thetransistor 55 is connected through a resistor 58 to ground, and thejunction of the resistor 58 and the base 1 electrode of the transistor55 is connected through a coupling capacitor 59 and a resistor 66 to oneinput of an operational amplifier 63. The amplifier 63 has two otherinputs, one of which is connected through a resistor 61 to a terminal65, and the other of which is connected through a resistor 62 to theoutput of the amplifier 63. An output terminal 64 is also connected tothe output of the amplifier 63.

In operation, the unijunction transistor 55 serves as a lowfrequencyoscillator. When the circuit of FIG. 8 is first energized, thetransistor 55 is nonconductive and the capacitor 54 is uncharged. Theterminal 51 is connected to the output of the amplifier 32 in FIG. 4,and when a positive potential is applied to the terminal 51, thecapacitor 54 begins charging toward that potential. When the potentialacross the capacitor 54 reaches the breakdown or triggering voltage ofthe transistor 55, that transistor conducts, drawing current from thesource connected to the terminal 57 and dropping the potential at itsbase 2 electrode due to the potential drop through the resistor 56.Conduction through the transistor 55 also reduces the resistance of thebase-emitter circuit, causing the capacitor 54 to discharge rapidlythrough that circuit. When the potential of the discharging capacitor 54drops below the triggering potential of the transistor 55, thattransistor becomes nonconductive, and the cycle begins again. From theabove, it becomes clear that the operation of the low-frequencyoscillator depends upon the presence of a positive potential havingsufficient amplitude to trigger the transistor 55 at the terminal 51.Thus, the operation of the oscillator in the rales generator of FIG. 8is synchronized with the generation of the exhalation portion 18 of thebreathing envelope. The output of the low-frequency oscillator is takenfrom the junction of the base 1 electrode and the resistor 58 and isapplied through the coupling capacitor 59 and the resistor 66 to oneinput of the amplifier 63. The network of resistors 66, 61 and 62comprises a summing network at the input to the amplifier 63, and whenthe terminal 65 is connected to the output of the breathing envelopegenerator of FIG. 4, the two signals from the two generators are summedin the amplifier 63.

To simulate the condition of rales, the generator of FIG. 8 mustgenerate short duration pulses which are superimposed upon the normalbreathing waveform from the circuit of FIG. 4. Thus, it is importantthat the two generators be synchronized. In addition, the potentialapplied to the input terminal 51 controls the frequency at which theshort duration pulses are generated by the circuit of FIG. 8. As thepotential applied to the terminal 51 increases, the time required forthe capacitor 54 to charge to trigger potential decreases. Thus, as theexhalation portion 18 of the complete breathing cycle rises to itsmaximum value, the frequency of the rales signals also increases. Theshort duration pulses generated by the circuit of FIG. 8 are shown inFIG. 9. When these signals are applied to a sound transducer, theyproduce the rasping sound heard in cases of rales. The switch 52 permitsthe insertion of the malady into the normal breathing envelope wheneverdesired to indicate the difference between normal breathing and abnormalbreathing as mentioned above. The waveform of the total sound is shownin FIG. l0 which shows the synchronization of the short duration pulsesof FIG. 8 and the breathing envelope of FIG. 4, and the manner in whichthe amplitude of the short duration pulses is added to the instantaneousamplitude of the breathing envelope. In the system shown in FIG. 8, theoutput of the circuit of FIG. 4 is applied to the input terminal 65, andthe output from the entire system is taken from the output terminal 64.Thus, when the switch 52 is closed, the output from the terminal 64 isthe waveform shown in FIG. 8, and when the switch 52 is open, the outputfrom the terminal 64 is that shown in FIG. 1.

This specification has described new and improved apparatus forgenerating waveforms of the sounds produced by animal bodies, inparticular human bodies. The apparatus described and illustratedindicates means for generating both I normal and abnormal soundwaveforms. It is realized that the above description may indicate tothose in the art additional ways in which the principles of thisinvention may be used without departing from its spirit. It is,therefore, intended that this invention be limited only by the scope ofthe appended claims.

What is claimed is:

l. A system for generating waveforms which duplicate those of normalbodily sounds, said system comprising means for generating a sine wave,means for distorting said sine wave to form a recurring wave of the samefrequency as said sine wave, an amplitude modulator, and means forsupplying a high-frequency signal and said recurring wave to saidmodulator so that said recurring wave amplitude modulates saidhighfrequency signal.

2. The system defined in claim ll wherein said distorting means includesa voltage adder, means for applying said sine wave to said adder, andmeans for applying a constant voltage to said adder to displace saidsine wave from its normal position symmetrical about its zero axis.

3. The system defined in claim 2 further including a first path and asecond path, a first diode connecting the output from said adder to saidfirst path to apply one polarity portion of said displaced wave to saidfirst path, and a second diode connecting the output from said adder tosaid second path to apply the other polarity portion of said wave tosaid second path.

4. The system defined in claim 3 wherein said first path furtherincludes an inverter to change the polarity of said one polarity portionso that the said one and said other portions are of the same polarity.

5. The system defined in claim 4 wherein said second path includesvoltage integrating means for lengthening said other portions withrespect to said one portion.

6. The system defined in claim 5 further including voltagecombiningmeans having at least two inputs and an output, means for connecting theoutput of said first and second paths to said inputs, amplifier meansconnected to said output, and means for connecting the output from saidamplifier means to said modulator.

9. The system defined in claim 8 wherein said means for modifying thewaveform comprises a summation amplifier having at least two inputs,means for connecting the output of said oscillator to one input andmeans for connecting the output of said modulator to the other input,the output of said summation amplifier providing said abnormalwaveforms.

10. The system defined in claim 9 wherein said oscillator generatespulses of short duration compared to said one portion.

1. A System for generating waveforms which duplicate those of normalbodily sounds, said system comprising means for generating a sine wave,means for distorting said sine wave to form a recurring wave of the samefrequency as said sine wave, an amplitude modulator, and means forsupplying a high-frequency signal and said recurring wave to saidmodulator so that said recurring wave amplitude modulates saidhigh-frequency signal.
 2. The system defined in claim 1 wherein saiddistorting means includes a voltage adder, means for applying said sinewave to said adder, and means for applying a constant voltage to saidadder to displace said sine wave from its normal position symmetricalabout its zero axis.
 3. The system defined in claim 2 further includinga first path and a second path, a first diode connecting the output fromsaid adder to said first path to apply one polarity portion of saiddisplaced wave to said first path, and a second diode connecting theoutput from said adder to said second path to apply the other polarityportion of said wave to said second path.
 4. The system defined in claim3 wherein said first path further includes an inverter to change thepolarity of said one polarity portion so that the said one and saidother portions are of the same polarity.
 5. The system defined in claim4 wherein said second path includes voltage integrating means forlengthening said other portions with respect to said one portion.
 6. Thesystem defined in claim 5 further including voltage-combining meanshaving at least two inputs and an output, means for connecting theoutput of said first and second paths to said inputs, amplifier meansconnected to said output, and means for connecting the output from saidamplifier means to said modulator.
 7. The system defined in claim 6further including means for modifying the waveforms generated by saidsystem to generate waveforms of abnormal body sounds, said meansincluding a switch for connecting said means with said system.
 8. Thesystem defined in claim 7 wherein said means for modifying the waveformscomprises an oscillator, means for connecting said oscillator to oneside of said switch, and means for connecting the other side of saidswitch to the output of said inverter so that said oscillator is biasedto operate only during said one portion of said waveform.
 9. The systemdefined in claim 8 wherein said means for modifying the waveformcomprises a summation amplifier having at least two inputs, means forconnecting the output of said oscillator to one input and means forconnecting the output of said modulator to the other input, the outputof said summation amplifier providing said abnormal waveforms.
 10. Thesystem defined in claim 9 wherein said oscillator generates pulses ofshort duration compared to said one portion.